Disk drive using servo in data technique

ABSTRACT

A disk drive stores overhead information corresponding to multiple servo sectors within a dedicated data sector in a customer data region of a data storage disk. The overhead information includes servo data for which the information content does not depend upon the physical location of the data on the disk surface. During a data storage operation, the overhead data is read from the dedicated data sector and stored in a buffer memory within the disk drive. A portion of the overhead data is then retrieved from the buffer memory for each servo sector subsequently traversed by the transducer for use in performing a data processing task related to the servo sector.

FIELD OF THE INVENTION

The invention relates generally to data storage systems and, moreparticularly, to disk-based data storage systems.

BACKGROUND OF THE INVENTION

A disk drive is a data storage device that stores data in concentrictracks on a disk shaped medium (i.e., a disk). A disk drive is generallyused as a mass storage device for an external host computer that isconnected to the disk drive via an input/output port. During normal diskdrive operation, the host computer delivers an access request (i.e., aread request or a write request) to the disk drive requesting a transferof customer data between the host computer and the disk. The disk drivethen performs the requested data transfer by performing either a readoperation (where data is transferred from the disk to the host computer)or a write operation (where data is transferred from the host computerto the disk). In the access request, the host computer generallyindicates a location on the disk surface from/to which the customer datais to be transferred. For example, the host computer can specify atarget track and sector on the disk or it can indicate a logical blockaddress from which a target track and sector can be calculated. The diskdrive then moves a transducer to a position above the identified disklocation and the transfer of customer data is initiated.

In addition to customer data, the surface of the disk in a disk drivenormally includes some non-customer data (i.e., overhead data) tofacilitate proper disk drive operation. For example, the disk surfaceusually includes servo data for use by the disk drive to position thetransducer during read and write operations. The servo data can includeamong other things: coarse position information (e.g., track address),and fine position information (e.g., servo bursts) for use indetermining transducer position, and correction information (e.g.,embedded runout correction (ERC) values) for use in compensating forrotational peculiarities in the disk structure. During disk driveoperation, the transducer periodically reads the servo data from thesurface of the disk. The disk drive then uses the servo data toappropriately move the transducer to the desired position.

As can be appreciated, proper disk drive operation depends on theaccurate and reliable reproduction of the servo data written on thedisk. Servo data has traditionally been written in radially alignedservo spokes occurring at equal intervals about the circumference of thedisk. The servo spokes are generally written during disk drivemanufacture by a highly accurate and very expensive piece of equipmentknown as a servo track writer (STW). Accordingly, the servo spokescannot be modified by the customer after disk drive delivery (i.e., theyare read-only). In addition, the information within the servo spokes iswritten at a different (i.e., lower) frequency from the other data onthe disk surface. Servo spokes have traditionally included a minimallevel of error detection capability, usually comprising a single paritybit. In contrast, customer data regions have generally used verysophisticated error detection/correction schemes to insure dataintegrity.

An ongoing trend in the disk drive industry is to store an everincreasing amount of data within a given area on a disk surface (i.e.,to increase disk data densities). Along with this increase in datadensity comes an increase in the difficulty with which servo data can beaccurately reproduced and utilized. Thus, current methods for storingservo information on the disk surface are rapidly becoming inadequate.In addition, current methods are generally expensive to implement (e.g.,STW costs) and do not permit servo re-calibrations to be performed inthe field. Current methods also make inefficient use of disk space asall servo information is generally written at a lower frequency and thustakes up a greater amount of disk surface area.

Therefore, there is need in the disk drive industry for new techniquesfor arranging and using servo data in a disk drive. The techniques willpreferably be highly reliable for use in high capacity disk drives andshould be relatively inexpensive to implement. In addition, thetechniques will preferably allow servo re-calibrations to be performedin the field. Furthermore, it is desirable that the techniques makerelatively efficient use of disk surface space.

SUMMARY OF THE INVENTION

The present invention relates to a disk drive that utilizes noveltechniques for storing, retrieving, and using servo data. The inventionrecognizes that the data traditionally stored in servo spokes is of twobasic types. A first type, referred to herein as VIPL data for “value isphysical location”, includes overhead data for which the informationcontent is tied to the physical location of the data on the disk. Aservo burst represents VIPL data, for example, because the indicationproduced by reading the burst, and thus the information derived from theburst, depends upon the positional relationship between the transducerand the burst at the time of the reading. A second type of data, knownas non-VIPL data, includes overhead data for which the informationcontent is not tied to the physical location of the data on the disk.That is, the data does not need to be located at the position on thedisk to which it applies. Embedded runout correction (ERC) data is anexample of non-VIPL data because the information derived from readingthe ERC data (i.e., runout values corresponding to particular locationson the disk) does not depend on the position of the data at the time ofthe reading.

In accordance with the present invention, some or all of the non-VIPLdata normally stored within the servo spokes of the disk is moved into aseries of “servo in data” or SID sectors within the customer dataregions of the disk. The SID sectors on the disk are similar to customerdata sectors in that they can have a preamble field, a synchronizationfield, a payload area, and error detection/correction information. TheSID sectors, however, do not have to have the same size as the customerdata sectors. In one embodiment, for example, the SID sectors are eachsignificantly smaller than a customer data sector. The SID sectorswithin a particular zone of the disk are all preferably located a fixedinterval of time from a nearest preceding servo spoke on the disk. Thisallows the SID sectors to be easily located during disk operations. Inaddition, the SID sectors on a disk can be of different sizes from oneanother and can be unevenly spaced about the disk.

The SID sectors are read using the same standard channel hardware thatis used to read the customer data sectors. However, in one embodiment ofthe invention, the SID sectors on a target track are read earlier in theseek/settle/track follow sequence than are the customer data sectors.This technique reduces the average latency involved with retrieving theSID data from the disk. In addition, the SID sectors on a disk can storedata redundantly on the disk (i.e., the same data in more than one SIDsector) to enhance system reliability.

In a preferred embodiment of the invention, each track of a data storagedisk includes a plurality of SID sectors that are each located within aseparate customer data region of the track. The number of SID sectors onthe track, however, is less then the number of servo spokes on thetrack. Each SID sector on the track includes non-VIPL data correspondingto multiple servo sectors on the track. For example, in one approach,embedded runout correction (ERC) data for multiple servo sectors on thetrack is stored within each SID sector. During a data transferoperation, while the transducer is track following on the track, one ofthe SID sectors is read by the transducer and the resulting ERC data isstored within a semiconductor memory in the disk drive. The stored ERCdata is then retrieved as needed as the transducer traverses subsequentservo sectors on the disk surface to perform appropriate servocorrection operations. When a subsequent SID sector is traversed by thetransducer, new ERC data is stored in the semiconductor memory and theprocess is repeated.

Moving non-VIPL data into the SID sectors provides many advantages overprior servo data schemes. For example, one advantage is a significantreduction in the amount of data that needs to be written by the STWduring disk drive manufacture. This decrease in STW use duringmanufacture can reduce the time and expense of disk drive fabricationconsiderably. Another benefit relates to the fact that the SID sectorsare written by the transducer within the disk drive and thus can berewritten at any time. This allows periodic re-calibrations to be doneon the SID data, which can significantly improve overall transducerpositioning performance. For example, ERC values stored in the SIDsectors can be periodically re-measured and rewritten during the life ofthe disk drive. As disk densities increase, this “tracking” of spindlerunout changes with time can be very valuable to servo positioningaccuracy.

Another advantage of the SID concept is that it allows a greater levelof error detection/correction to be used to protect the non-VIPL datawithin the SID sector than has traditionally been available within theservo spokes. This increased error handling functionality can greatlyimprove servo reliability. A further advantage relates to the fact thatdata in the servo spokes of the disk are normally stored at lowerfrequencies than the customer data, thereby utilizing more disk area tostore a given amount of data. By moving the non-VIPL data to thecustomer data regions, the same amount of data can now be stored in asmaller amount of disk space. In yet another advantage, the non-VIPLdata from multiple servo spokes can be grouped together in a single SIDsector on a track so that it is all read, processed, and stored in a RAMmemory at the same time. The data is then available a priori when thecorresponding servo spokes are traversed by the transducer. Many otheradvantages of the inventive principles will become apparent in light ofthe following description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a disk drive that can utilize theprinciples of the present invention;

FIG. 2 is a top view of a data storage disk illustrating a typical datastorage configuration;

FIG. 3 is a top view of a data storage disk illustrating a data storageconfiguration in accordance with one embodiment of the presentinvention;

FIG. 4 is a diagram illustrating a data storage configuration within adata storage track in accordance with one embodiment of the presentinvention;

FIG. 5 is a diagram illustrating a data storage configuration within adata storage track in accordance with another embodiment of the presentinvention;

FIG. 6 is a diagram illustrating two successive tracks used in asequential data transfer operation in accordance with one embodiment ofthe present invention; and

FIG. 7 is a diagram illustrating two successive tracks used in asequential data transfer operation in accordance with another embodimentof the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention relates to a disk drive that utilizes noveltechniques for storing, retrieving, and using servo data. The disk driveuses a series of “servo in data” or SID sectors within the customer dataregions of the disk(s) to store overhead data for which the informationcontent is not tied to the physical location of the data on the disk.Thus, the servo spokes of the disk can be made appreciably shorter(quicker in time) because the data within the SID sectors are written atthe higher customer data frequencies rather than the lower overhead datafrequency used within the servo spokes, and thus occupy a smaller areaon the disk surface, a reduction in the overall amount of disk spaceoccupied by the non-VIPL data can be achieved. Like ordinary customerdata, the SID data within the SID sectors can be repeatedly rewritten bythe customer after purchase. In addition, the SID data can be protectedby a higher level of error detection/correction than is normallyavailable in the servo spokes, although the high levels used forprotecting customer data do not have to be implemented in the SIDsectors. The inventive principles also allow a significant portion ofthe data detection functionality to be moved from the channel to thecontroller chip of the disk drive, thus giving the disk drivemanufacturer greater control over the design process. In addition, theinventive techniques allow a disk drive designer to trade overhead spacefor data latency in a predictable manner.

FIG. 1 illustrates a disk drive 10 that can utilize the principles ofthe present invention. In the discussion that follows, the basicoperation of the disk drive 10 will be described before a description ofthe invention is undertaken. As illustrated, the disk drive 10 iscoupled, via input/output port 14, to an external host computer 12 whichuses the disk drive 10 as a data storage device. The host 12 deliversdata access requests to the disk drive 10 via port 14. In addition, port14 is used to transfer customer data between the disk drive 10 and thehost 12 during read and write operations. The disk drive 10 includes: adisk 16, a transducer 18, an actuator arm 20, a voice coil motor (VCM)22, a controller 24, a read/write channel 26, and an interface 28. Thedisk 16 is a data storage medium that stores data in substantiallyconcentric data storage tracks on a surface of the medium. In a magneticdisk drive, for example, the data is stored in the form of magneticpolarity transitions within each track. Data is “read” from the disk 16by positioning the transducer 18 above a desired track of the disk 16and sensing the data stored within the track as the track moves belowthe transducer 18. Similarly, data is “written” to the disk 16 bypositioning the transducer 18 above a desired track and delivering awrite current representative of the desired data to the transducer 18 atan appropriate time.

The actuator arm 20 is a semi-rigid member that acts as a supportstructure for the transducer 18, holding it above the surface of thedisk 16. The actuator arm 20 is coupled at one end to the transducer 18and at another end to the VCM 22. The VCM 22 is operative for impartingcontrolled motion to the actuator arm 20 to appropriately position thetransducer 18 with respect to the disk 16. The VCM 22 operates inresponse to a control signal i_(control) generated by the controller 24.The controller 24 generates the control signal i_(control) in responseto an access command received from the host 12 via the interface 28.

The read/write channel 26 is operative for appropriately processing thedata being read from/written to the disk 16. For example, during a readoperation, the read/write channel 26 converts an analog read signalgenerated by the transducer 18 into a digital data signal that can berecognized by the controller 24. The channel 26 is also generallycapable of recovering timing information from the analog read signal.During a write operation, the read/write channel 26 converts customerdata received from the host 12 into a write current signal that isdelivered to the transducer 18 to “write” the customer data to anappropriate portion of the disk 18. As will be discussed in greaterdetail, the read/write channel 26 is also operative for continuallyprocessing data read from servo spokes on the disk 16 and delivering theprocessed data to the controller 24 for use in, for example, transducerpositioning.

FIG. 2 is a top view of a magnetic storage disk 30 illustrating atypical organization of data on the surface of the disk 30. As shown,the disk 30 includes a plurality of concentric data storage tracks 32for use in storing data on the disk 30. The data storage tracks 32 areillustrated as center lines on the surface of the disk 30; however, itshould be understood that the actual tracks will each occupy a finitewidth about a corresponding centerline. The data storage disk 30 alsoincludes a plurality of radially aligned servo spokes 34 that each crossall of the tracks 32 on the disk 30. The servo spokes 34 each includeservo information that is read by the transducer 18 during disk driveoperation for use in positioning the transducer 18 above a desired trackof the disk 30. The track portions between servo spokes 34 havetraditionally been used to store customer data received from, forexample, the host computer 12 and are thus referred to herein ascustomer data regions 36. The customer data regions 36 on a track arenormally subdivided into fixed length data units referred to herein ascustomer data sectors (not shown in FIG. 1). In addition to the above,the magnetic storage disk 30 may include a plurality of recording“zones” that each store customer data at a different recordingfrequency. This zoned approach takes advantage of the longer physicallength of the outer tracks of the disk to store a larger amount ofcustomer data. It should be understood that the number of tracks 32 andservo spokes 34 shown on the surface of the disk 30 of FIG. 2 have beenmade relatively low for illustration purposes. That is, modern diskdrives normally use data storage disks having a considerably largernumber of tracks and servo spokes.

The data within the servo spokes 34 of a disk 30 are normally writtenduring disk drive manufacture by a special piece of equipment known as aservo track writer (STW). A STW is a very precise piece of equipmentthat is capable of writing data on the disk surface with a high degreeof positional accuracy. In general, a STW is a very expensive piece ofcapital equipment. Thus, it is generally desirable that a STW be used asefficiently as possible during manufacturing operations. Even a smallreduction in the amount of data needed to be written by the STW per diskcan result in a significant cost and time savings.

Once a disk drive has been sealed during manufacture, the overhead datain the servo spokes 34 of the disks within the drive is never rewritten.That is, the overhead data is stored in a “read only” state within theservo spokes. Conversely, the customer data stored within the customerdata regions 36 can be written and repeatedly rewritten by the customer.The data within the customer data regions 36 of a track are generallystored at a higher frequency than the data stored within the servospokes 34 of the same track and thus more data can be stored in a givenamount of disk area in the customer data regions 36. In addition, indisk drives implementing constant linear density (CLD) or zonedarrangements, the data frequency in the customer data regions 36increases with radial distance over the disk surface while the datafrequency within the servo spokes remains the same over the surface ofthe disk 30.

As described above, the read/write channel 26 of the disk drive 10processes data read from the servo spokes 34 of the disk 16 differentlyfrom data read from the customer data regions 36 of the disk. Forexample, with reference to FIG. 1, the data read from the servo spokes34 is delivered to the controller 24 via a serial data line 40 whiledata read from the customer data regions 36 are delivered to thecontroller 24 over the faster parallel data line 42. Customer datareceived by the controller 24 on parallel line 42 during a readoperation is usually directly transferred to the host 12, in parallelform, via interface unit 28. The servo data received by the controller24 via serial line 40 is used within the controller 24 to, among otherthings, develop the control signal i_(control) for delivery to the VCM22 to control transducer positioning.

In conceiving of the present invention, it was appreciated that someoverhead data stored on the disk 16 (referred to herein as “VIPL” datafor “value is physical location”) communicates information to thecontroller 24 based on the precise physical location of the data read bythe transducer 18 while other overhead data on the disk 16 (referred toherein as “non-VIPL” data) communicates literal information to thecontroller 24 that does not need to be stored at the location of theservo spoke on the disk that it applies to. It was thus determined thatsignificant advantages could be achieved if the amount of non-VIPL datastored within the servo spokes of the disk (i.e., the data written bythe STW) was reduced. In accordance with the present invention,therefore, some or all of the non-VIPL data traditionally stored withinthe servo spokes of the disk is moved to dedicated areas within thecustomer data regions 36 of the disk 16.

Transferring non-VIPL data to the customer data regions 36 of the disk16 provides many advantages. One advantage is that the amount of datathat needs to be written by the STW is significantly reduced. Asdescribed above, STW time is a very costly commodity and any reductionin STW usage during disk drive assembly will reduce disk drivemanufacturing costs and assembly times. Another advantage is that thenon-VIPL data written in the customer data regions is capable of beingrewritten in the field by the user. This ability can be valuable, forexample, should the data be accidently corrupted during disk driveoperation. The ability to rewrite the data can also be used to implementperiodic recalibration of certain non-VIPL information (e.g., runoutdata) during the life of the disk drive.

A third benefit of moving non-VIPL data to the customer data regions 36of the disk 16 is that data that has historically been exclusivelyprocessed within the read/write channel 26 can now be processed at leastpartially within the controller 24 of the disk drive. As is well knownin the disk drive industry, disk drive manufacturers normally contractchannel design tasks out to companies that specialize in the design ofdisk drive channel chips. Disk drive controllers, on the other hand, arenormally developed in-house by the disk drive manufacturers. By movingnon-VIPL data into the customer data regions of the disk, a largeramount of data can now be processed within the controller 24 of thedrive, thus giving the disk drive manufacturer more control over thedesign process and reducing product cycle times. For example, a singlerepetitive runout correction solution can be implemented in thecontroller 24 rather than having multiple channel vendors developindependent runout solutions within the channel chips. In addition,servo enhancements and additions can be accomplished without requiringan expensive channel redesign by the vendor.

A further advantage comes from the fact that data in the servo spokes ofthe disk are normally stored at lower frequencies, thereby utilizingmore disk area to store a given amount of data. By moving non-VIPL datato the customer data regions, a given amount of data can be stored usinga smaller amount of disk space and using standard customer datarecording technologies. In yet another advantage, the non-VIPL data frommultiple servo sectors can be grouped together in a single SID sector ona track so that they are all read and stored in a RAM memory at the sametime. The data is then available a priori when the corresponding servosectors are traversed by the transducer 18. As will be apparent from thediscussion that follows, the principles of the present invention alsoprovide many other benefits and advantages.

FIG. 3 is a top view of a magnetic storage disk 50 illustrating anorganization of data on the surface of the disk 50 in accordance withone embodiment of the present invention. As with the disk 30 of FIG. 2,the disk 50 includes a plurality of concentric data storage tracks 32, aplurality of radially aligned servo spokes 34, and a plurality ofcustomer data regions 36. The disk 50 may also utilize a CLD or zonedapproach for storing customer data. However, unlike the previouslydescribed disk 30, the disk 50 of FIG. 3 also includes a plurality of“Servo In Data” (SID) sectors 44 in the customer data regions 36 thatare used to store non-VIPL data that was formally located within theservo spokes 34. Because non-VIPL data was moved out of the servo spokes34 and into the SID sectors 44, the servo spokes 34 can be made narrower(shorter in time), thus occupying less area on the surface of the disk50. In addition, because the data in the customer data regions 36 iswritten at a higher frequency than the data in the servo spokes 44, lessdisk area is used to write the non-VIPL data in the SID sectors 44 thanwas used previously to write the data in the servo spokes 44. Forreasons that will soon become apparent, the number of SID sectors 44 ona track 32 is preferably less than the number of servo spokes 34 on thetrack.

FIG. 4 is a diagram illustrating a portion of a data track 52 from adisk utilizing SID-based storage techniques (e.g., disk 50 of FIG. 3).As illustrated, the track 52 includes multiple servo sectors 54 and acustomer data region 56 between each successive pair of servo sectors54. Each customer data region 56 includes at least a portion of acustomer data sector 60. As illustrated, each customer data sector 60can be an uninterrupted sector (such as customer data sectors B and C)or a split data sector (such as customer data sectors A and D). Selectedcustomer data regions 56 on the track 52 also include a SID sector 58for storing non-VIPL overhead data corresponding to at least one (andpreferably more) of the servo sectors 54 on the track 52. As describedabove, in a preferred embodiment, less than all of the customer dataregions 56 on the track 52 include a SID sector 58.

In one embodiment of the invention, the SID sectors on a track are eachpositioned a fixed time period (with respect to disk rotation) from aprevious servo sector mark on the same track so that the SID sectors canbe easily located during disk drive operations. For example, withreference to FIG. 4, the SID sector 58 is positioned immediately after(in the direction of relative transducer movement 38) a correspondingservo sector 54. Thus, all SID sectors 58 on the track 52 would occurimmediately after a nearest servo sector (as in disk 50 of FIG. 3).Preferably, all of the SID sectors on the entire disk will be locatedthe same fixed time period from a preceding servo sector mark; however,in a zoned system, the fixed time periods may change from zone to zone.Virtually any fixed time period can be used in accordance with thepresent invention, as long as the corresponding SID sector 58 will fitfully within the subsequent customer data region 56. That is, the SIDsectors 58 can be placed at the beginning, the end, or at someintermediate position within the customer data region 56.

In an alternative embodiment, the SID sectors are placed within theformat holes between customer data sectors on each track. In this case,a more complex SID sector location algorithm needs to be implemented tofind the SID sectors within a particular track during disk driveoperations. In one approach, for example, a semiconductor lookup tableis implemented for locating the format holes on a particular trackduring read and/or write operations. As will be apparent to a person ofordinary skill in the art, other methods for tracking the location ofthe format holes also exist.

As described above, in a preferred embodiment of the invention, thenumber of SID sectors on a track of a disk is less than the number ofservo sectors on the track. For example, with reference to FIG. 4, a SIDsector 58 occurs after one servo sector 54 on the track 52 but not aftera subsequent servo sector 54. In such an arrangement, the SID sector 58preferably carries non-VIPL data corresponding to all of the servosectors 54 between the SID sector 58 and a next SID sector 58 on thetrack 52 (in the direction of relative transducer movement 38). Duringdisk drive operation, while the transducer 18 is track following on thetrack 52, the transducer 18 reads the SID sector 58 and the controller24 causes the resulting SID data to be temporarily stored in asemiconductor buffer memory. The controller 24 then retrievesappropriate portions of the SID data from the buffer memory forprocessing as the transducer 18 traverses each of the subsequent servosectors 54 on the track 52 until the next SID sector 58 is reached.Because the SID data has already been processed by the read/writechannel 26 before it is stored in the buffer memory and is readilyavailable in the memory in the proper format before each of thesubsequent servo sectors 54 are reached by the transducer 18, servoprocessing for the subsequent servo sectors 54 is performed much morerapidly than in systems of the past that stored the data within theassociated servo sector. In addition, because each of the SID sectors 58on the disk requires a minimal amount of overhead to enable thetransducer to accurately read the data within the sector 58 (e.g.,preamble and synchronization fields), storing non-VIPL datacorresponding to multiple servo spokes 54 into a single SID sector 58makes efficient use of the overhead data.

As illustrated in FIG. 3, the SID sectors 44 can be unequally spacedabout the disk 50. That is, the distance between adjacent SID sectors 44does not have to be uniform about the disk 50. Likewise, the SID sectors58 on a track do not all have to include the same amount of data.Unequal SID sector spacing/size may be desired, for example, so that thelogical data sectors properly align with the physical data sectors onthe track.

In general, the disk drive controller 24 should always be able todetermine the location of the next SID sector 58 on a track so that itknows when to store the corresponding SID data in the buffer memory. Ina system using equally spaced SID sectors 58, the task is relativelysimple because the controller 24 just needs to remember the fixed numberof servo sectors 54 between successive SID sectors 58. A counter canthen be used to count servo sectors 54 to find a subsequent SID sector58. If unequally spaced SID sectors are used, however, SID sectorlocation can be more complicated. In one embodiment of the invention,each SID sector 58 includes a field indicating the distance from thepresent SID sector to a subsequent SID sector on the track 52. Thisfield can include, for example, a digital value specifying the number ofservo sectors between the present SID sector and the subsequent SIDsector. In a system where only one SID sector spacing per track isdifferent from the others, a simple flag bit can be used to identify theSID sector preceding the unequal interval. When the controller 24detects the flag bit, it knows to use a different counter value tolocate the subsequent SID sector. Other methods for tracking SIDlocations are also possible.

In one embodiment of the invention, the SID sectors 58 on each track 52of a data storage disk include redundant data. That is, multiple SIDsectors 58 within a track 52 each have duplicate non-VIPL overhead datacorresponding to a particular servo sector on the track. In oneapproach, for example, data from each servo sector on a track is storedin at least two different SID sectors on the track. In another approach,each SID sector on a track includes servo data from every servo sectoron the same track so that the controller 24 has access to data for everyservo sector on the track after reading a single SID sector. Byproviding data redundancy, the chances that non-VIPL data for aparticular servo sector will be irretrievably lost is significantlyreduced. For example, if data corresponding to a particular servo sectoris lost from one SID sector on a track, the data can be easily retrievedfrom another SID sector on the same track and rewritten into the firstSID sector.

Another advantage of the SID concept is that it allows a greater levelof error detection/correction to be used to protect the non-VIPL datawithin the SID sector than is traditionally used within a servo sector.Servo sectors, for example, generally use a minimal “parity” approach toerror detection. The SID sector, on the other hand, can utilize a morepowerful error detection/correction technique, such as those typicallyused in customer data sectors. In one embodiment of the invention, thelevel of error detection/correction that is used within the SID sectorsis less than that used in the customer data sectors (to reduce overhead)but considerably more than that used in the servo spokes (i.e., a paritybit). For example, if overhead is an overriding concern, a minimalcyclic redundancy check (CRC) approach can be implemented in the SIDsectors. If greater error protection is required, a scaled back errorcorrectional code (ECC) can be used.

In accordance with the present invention, virtually any form of non-VIPLoverhead data that is traditionally associated with the servo spokes ofa disk drive can be stored within the SID sectors of the disk. This caninclude, for example, embedded runout correction (ERC) data, servosector identification data, reliability information, development debuginformation, and diagnostic information. In addition, data correspondingto the overall track, such as average runout and servo defect managementinformation, can also be stored in the SID sectors. A SID sector dataconfiguration is preferably defined that allows the controller 24 toeasily determine which data read from a SID sector corresponds with aparticular servo sector on the track. In one embodiment, for example,the controller 24 knows the precise number of data bytes within a SIDsector that correspond to each servo sector on the track. Thus, a firstblock of bytes of that size are used in connection with a firstsubsequent servo sector, a second block of bytes of that size with anext subsequent servo sector, and so on. In another approach, servosector addresses are associated with the SID data to facilitate properapplication of the data. Other techniques for matching SID data tocorresponding servo sectors also exist.

In one aspect of the invention, a considerable reduction in overhead isachieved by eliminating from the disk some or all of the data in theservo sector that has traditionally been used to facilitate accurateretrieval of servo information from the servo sectors. For example,servo sectors of the past have generally included fields such as apreamble field, a synchronization (sync) field, a spin tolerance field,a parity field, and a data closure field to help the disk driveaccurately read the payload data within the servo sector. Because therewas a considerable amount of payload data within each servo sector, thelikelihood of read errors was relatively high and the additionaloverhead was deemed necessary for proper data retrieval. However,because the amount of payload data within the servo sectors can bereduced dramatically using the principles of the present invention, theamount of overhead data required to accurately reproduce the payloaddata can be reduced accordingly. In one embodiment of the invention, forexample, the servo sector payloads include only a shortened trackaddress (Gray code) and the ABCD servo bursts. In such an embodiment,only a minimal amount of overhead is needed to ensure accurate servosector reproduction. The SID contains the full track address andcorrections for fine position bursts.

Referring back to FIG. 1, a significant benefit of the present inventionis that the non-VIPL data stored in the SID sectors are treated likeordinary customer data by the read/write channel 26. Thus, after thedata is detected, it is transferred to the controller 24 via paralleldata line 42, using the standard handshake, rather than over the slowerserial data line 40. The controller 24 thereafter stores the data in abuffer memory for later use. Because a SID sector is generally adifferent length than a customer data sector, a special counter forbytes transferred and an address pointer to the buffer memory isnormally required. The buffer memory can include a dedicatedsemiconductor memory element or a portion of an existing buffer spacecan be used. The size of the buffer space depends upon the SID data andservo algorithms.

In one embodiment of the present invention, the SID sectors are used tostore embedded runout correction (ERC) values. Each SID sector includesa predetermined number of ERC values corresponding to an equal number ofsubsequent servo sectors on the same track. The controller 24 reads theERC values from the SID sector and stores the values within a buffermemory. Then, as each subsequent servo sector approaches, the controller24 retrieves a corresponding ERC value from the buffer and uses it togenerate the control signal i_(control) that is delivered to the VCM 22.

FIG. 5 illustrates a SID configuration that is used on a track 76 in oneembodiment of the invention. As shown, the track 76 includes a pluralityof servo sectors 78 and a plurality of customer data regions 80 that areeach located between two adjacent servo sectors 78. The track 76 alsoincludes a plurality of read SID sectors 82 having ERC values for useduring read operations and a plurality of write SID sectors 84 havingERC values for use during write operations. Each of the read and writeSID sectors 82, 84 includes 5 ERC values corresponding to 5 subsequentservo sectors on the track 76 (although the number of values can vary).In addition, the read and write SID sectors 82, 84 alternate on thetrack 76. As illustrated in FIG. 5, if a dual element transducer havinga lateral offset between the read and write element is used, the readand/or write SID sectors 82, 84 can be offset from the track centerlineto compensate for the offset between the elements (i.e., by the read andwrite microjog values, respectively).

In one embodiment of the present invention, SID data corresponding toservo sectors on one track is stored within one or more SID sectors onanother track for use during multi-track sequential read and/or writeoperations. In a conventional read or write operation, a single block ofcustomer data is transferred from/to a single identified customer datasector on a disk surface. In a sequential read or write operation, onthe other hand, multiple customer data blocks are transferred from/tothe disk(s) in a disk drive in a single operation. The multiple customerdata blocks are read from or written to a plurality of sequentiallylocated customer data sectors on the surface(s) of the disk(s) using apredetermined sequential pattern that is specific to the particular diskdrive.

In a typical sequential read operation, for example, a host computerwill request that the disk drive read a predetermined number of customerdata sectors starting at a specific logical block address (LBA) in thedisk drive. The disk drive then moves a corresponding transducer to acustomer data sector corresponding to the specified LBA and reads therequested number of data sectors from that point on by following thepredetermined sequential pattern of the locations on the disk drivespecified by surface number and track number on a surface and sectornumber on a track. In one possible pattern, for example, the disk drivewill read successive customer data sectors within the track of thespecified LBA until a last data sector in the track is reached afterwhich it moves to a next track on the same disk surface and then a nexttrack until a last track on that disk surface is reached. The disk drivewill then switch to a track on a next disk surface that is within thesame cylinder as the last track on the first disk surface and thesequential read will continue backwards through the tracks on the newdisk surface, and so on. In another possible pattern, the disk drivewill read successive customer data sectors within the track of thespecified LBA until a last sector is reached and will then switch toanother track within the same cylinder as the present track but on anext disk surface. The disk drive will then switch from track to trackwithin the cylinder until a last disk surface has been reached, afterwhich the disk drive changes to a new track on the last disk surface andmoves back through the disk surfaces in the new cylinder.

Naturally, the disk drive will only follow the predetermined pattern asfar as necessary to complete the requested operation, regardless of theparticular sequential pattern used. Thus, a particular sequentialoperation may involve a single track, multiple tracks on a single disksurface, or multiple tracks on multiple disk surfaces. As can beappreciated, a large number of different sequential patterns arepossible. The sequential pattern that is used in a particular disk driveis generally determined during disk drive design and is normallytransparent to the host.

As described above, in accordance with one embodiment of the invention,SID information for a “next track” in a multi-track sequential diskoperation is stored within a present track. Thus, the SID information isread and available for use before the transducer reaches the next trackin the sequential pattern (or, in a case where the next track is onanother disk, before control is switched to a different transducer). Byhaving the SID data buffered and ready for use a priori, servo dataprocessing on the new track is accelerated and problems relating totransducer latency are avoided. This technique can significantlyincrease the speed and accuracy of sequential read and write operationsand can be used regardless of the specific sequential pattern that isimplemented within the disk drive.

FIG. 6 is a diagram illustrating a pair of tracks 100, 110 that can beused during sequential read and write operations in a disk drive inaccordance with the present invention. For purposes of convenience, allfurther discussion will be with respect to sequential read operations,although the concepts are equally applicable to sequential writeoperations. As shown, each of the tracks 100, 110 includes a pluralityof servo sectors 102 and a plurality of customer data regions 104. Asdiscussed previously, the customer data regions 104 each include atleast a portion of a customer data sector (not shown in FIG. 6). Inaddition, as described previously, each track 100, 110 includes aplurality of write SID sectors 106 and a plurality of read SID sectors108 that each include SID data corresponding to the tracks on which thesectors 106, 108 are located.

During a sequential read operation, for example, the disk drivesequentially reads the customer data sectors on the present track 100until the end 112 of a last customer data sector on the present track100 is reached. The disk drive then positions to the next track 110 andbegins to read customer data sectors on the next track 110 at a point114 where a first customer data sector on the next track 110 begins. Asis customary in sequential disk operations, a skewed track arrangementis implemented in the disk drive where the first customer data sector(e.g., the sector starting at point 114 on track 110) on each track isoffset from (i.e., not radially aligned with) those on the other tracksof the disk(s). This skewing is used so that a reduced amount of latencyis experienced when switching from one track to the next during asequential operation (whether or not the next track is located on thesame or different disk surface). That is, a minimal distance is allowedfor the transducer to reliably seek to and settle on the next track 110before the first customer data sector on the new track 110 is reached.

As illustrated, for this embodiment, a pair of “next track” SID sectors116, 118 are located within the present track 100 that each include SIDdata corresponding to servo sectors 102 in the next track 110. Thus,during a sequential read operation, for example, the disk drive readsand stores the SID data located in the read “next track” SID sector 108on the present track 100 before switching to the next track 110. Thus,after the switch is made, the data is already available in a memory foruse in performing servo functions on the next track 110. Therefore, thedisk drive is able to perform, for example, ERC corrections at the servosectors on the next track 110 without having read a corresponding SIDsector 108 on the next track 110 (which might have required an entirerevolution of the disk). As can be appreciated, this can significantlyincrease transducer positioning accuracy on the next track 110 beforethe starting point 114 of the first customer data sector thereon isreached and may allow the skew distance to be reduced.

In a preferred approach, the “next track” SID sectors 116, 118 arelocated in the SID sector positions immediately preceding the lastcustomer data sector on the track. If these SID sector positions arealready taken by “same track” SID sectors 106, 108, than the SID sectorpositions preceding the “same track” SID sectors 106, 108 willpreferably be used for the “next track” SID sectors. Each track in thedisk drive will generally include at least one “next track” SID sectorfor the next track in the sequential pattern, regardless of whether thenext track is located on the same or a different disk surface. In oneapproach, the “next track” SID sector includes SID data corresponding tothe entire next track, although “next track” SID sectors includingpartial next track information can also be implemented in accordancewith the present invention. For example, the “next track” SID sectorsmay only include data for a transition region on the next track 110during which the transducer is seeking to and settling on the nexttrack.

In one embodiment, identification information (e.g. a flag bit) isstored in the SID sectors to identify whether they are for the presenttrack or for the next track. Alternatively, or in addition, informationmay be provided in each SID sector identifying whether the next SIDsector on the same track is for the present track or for the next track.As described above, each SID sector can also indicate the distance tothe next SID sector on the same track.

In some cases, it will be desirable to distribute “next track” SID dataover multiple SID data sectors on a present track. For example, in asituation where all of the possible SID sector locations on a presenttrack are occupied by “same track” SID sectors, it will generally bedesirable to spread out the “next track” SID data over some or all ofthe present track SID sectors. FIG. 7 is a diagram illustrating a pairof successive tracks 120, 122 for use in a sequential disk operationthat each include same track read SID sectors 124 and same track writeSID sectors 126 that each have a span of two servo spokes. Thus, everypossible SID sector location on the two tracks 120, 122 includes a “sametrack” SID sector 124, 126. In this embodiment, the “next track” SIDdata is distributed among the “same track” SID sectors 124, 126 on thepresent track 120. In addition, because a sequential disk operationmight be initiated with a partial track read or write on the presenttrack 120, the next track SID data is stored in the “same track” SIDsectors 124, 126 on the present track 120 in reverse order. That is,values for the first servo sectors 140, 142 after the start point 132 onthe next track 122 are stored in the last SID sectors 144, 146 on thepresent track 120. Values for the next servo sectors 148, 150 on thenext track 122 are stored in the next to last SID sectors 152, 154 onthe present track 120, and so on. Preferably, the next track SID datastored on the present track 120 will include identification informationidentifying the corresponding servo sectors on the next track 122.

The principles of the present invention can be applied in disk drivesusing virtually any form of servoing arrangement. For example, theinvention can be used in drives utilizing a constant linear density(CLD) scheme, a zoned arrangement, split data sectors, constant datafrequency systems, and even systems that use STW written servo sectorsthat are not radially aligned (i.e., not arranged in spokes). Inaddition, the SID sectors of the present invention can also be used tostore data that was not traditionally stored in the servo spokes becauseof concerns about increased overhead. Furthermore, the principles of theinvention can be extended to provide an additional reduction in overheadby further concentrating the SID data, such as by utilizing a single SIDsector per track, a single SID sector per group of tracks (e.g., perzone), or a single SID sector per disk surface.

Although the present invention has been described in conjunction withits preferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art readily understand.For example, the SID sectors of the present invention do not have toradially aligned into a “spoke” arrangement as shown in the illustratedembodiment. Such modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.

1. A disk drive comprising: a data storage disk having a plurality ofsubstantially concentric tracks, each of said plurality of substantiallyconcentric tracks having a plurality of servo sectors and a plurality ofcustomer data regions distributed therein, said plurality of servosectors including data that is recorded at a first frequency and saidplurality of customer data regions including data that is recorded at asecond frequency that is different from said first frequency, wherein atleast one of said customer data regions on said data storage diskincludes a dedicated portion for storing overhead data corresponding tomultiple servo sectors on said data storage disk and wherein said atleast one customer data region is located on a different track from saidmultiple servo sectors, said overhead data being recorded at said secondfrequency; a spin motor for rotating said data storage disk about anaxis; a transducer for use in transferring data between said datastorage disk and an exterior environment; an actuator assembly coupledto said transducer for use in moving said transducer to a target trackof said data storage disk to perform a data transfer with the targettrack, said actuator assembly including an actuator arm for supportingsaid transducer and a motor unit for controllably moving said actuatorarm in response to a control signal; and a controller for controllingthe operation of said disk drive, said controller receiving saidoverhead data after it has been read by said transducer, storing saidoverhead data in a buffer memory, and subsequently using a portion ofsaid overhead data stored in said buffer memory in response to traversalof one of said multiple servo sectors on said disk by said transducer toenhance disk drive performance.
 2. The disk drive, as claimed in claim1, wherein: said data that is recorded at a first frequency within saidplurality of servo sectors is written using a servo track writer duringdisk drive manufacture.
 3. The disk drive, as claimed in claim 1,wherein: said data that is recorded at a second frequency is writtenusing said transducer.
 4. The disk drive, as claimed in claim 1,wherein: said controller is operative for generating said control signalthat is input to said motor unit, wherein said controller uses saidportion of said overhead data to modify said control signal in responseto traversal of said one of said multiple servo sectors by saidtransducer.
 5. The disk drive, as claimed in claim 1, wherein: saidoverhead data includes embedded run out correction (ERC) data.
 6. Thedisk drive, as claimed in claim 1, wherein: said overhead data includesservo sector identification information.
 7. The disk drive, as claimedin claim 1, wherein: said overhead data includes disk drive datareliability information.
 8. The disk drive, as claimed in claim 1,wherein: said overhead data includes diagnostic information.
 9. The diskdrive, as claimed in claim 1, wherein: said at least one customer dataregion is located on a common track with said multiple servo sectors.10. The disk drive, as claimed in claim 1, wherein: each of saidplurality of substantially concentric tracks includes at least onecustomer data region having a dedicated portion for storing overheaddata corresponding to multiple servo sectors within said track.
 11. Thedisk drive, as claimed in claim 10, wherein: each of said plurality ofsubstantially concentric tracks includes multiple customer data regionsthat each have a dedicated portion for storing overhead datacorresponding to multiple servo sectors within said track.
 12. The diskdrive, as claimed in claim 11, wherein: said dedicated portions withinsaid multiple customer data regions in a first substantially concentrictrack are each located a fixed time period from a preceding servo sectormark within said track, with respect to a rotation speed of said datastorage disk.
 13. The disk drive, as claimed in claim 11, wherein: saidmultiple customer data regions within each substantially concentrictrack represent less than all of said customer data regions within saidtrack.
 14. The disk drive, as claimed in claim 11, wherein: saidmultiple customer data regions within each substantially concentrictrack are unevenly distributed about said substantially concentrictrack.
 15. A disk drive comprising: a data storage disk having aplurality of substantially concentric tracks, a first track within saidplurality of substantially concentric tracks having a plurality of servosectors and a plurality of customer data regions distributed therein, asubgroup of said plurality of customer data regions each including a SIDsector for storing overhead data corresponding to a predetermined numberof servo sectors on said first track, wherein multiple SID sectorswithin said first track include overhead data corresponding to a firstservo sector within said first track; a spin motor for rotating saiddata storage disk about an axis; a transducer for use in transferringdata between said data storage disk and an exterior environment; anactuator assembly coupled to said transducer for use in moving saidtransducer to a target track of said data storage disk to perform a datatransfer with said target track, said actuator assembly including anactuator arm for supporting said transducer and a motor unit forcontrollably moving said actuator arm in response to a control signal;and a controller for controlling the operation of said disk drive, saidcontroller receiving overhead data read from a first SID sector on saidfirst track by said transducer and using said overhead data to controlsaid disk drive in response to subsequent traversal by said transducerof each of said predetermined number of servo sectors associated withsaid first SID sector.
 16. The disk drive, as claimed in claim 15,wherein: said controller includes a buffer memory for temporarilystoring said overhead data read from said first SID sector afterreceipt.
 17. The disk drive, as claimed in claim 15, wherein: saidcontroller is operative for generating said control signal that isdelivered to said motor unit for positioning said transducer, whereinsaid controller uses said overhead data read from said first SID sectorto generate said control signal.
 18. The disk drive, as claimed inclaim, 15 wherein: said SID sectors within said first track are eachlocated a common distance from a corresponding preceding servo sectorwithin said first track.
 19. The disk drive, as claimed in claim 15,wherein: said SID sectors within said first track are each locatedadjacent to a nearest servo sector within said first track.
 20. The diskdrive, as claimed in claim 15, wherein: said SID sectors within saidfirst track each include a value indicative of a distance to asubsequent SID sector within said first track.
 21. The disk drive, asclaimed in claim 15, wherein: said SID sectors within said first trackeach include an embedded run out correction (ERC) value for each of saidpredetermined number of servo sectors associated with said SID sector.22. The disk drive, as claimed in claim 21, wherein: said SID sectorswithin said first track are divided into a first group of SID sectorsand a second group of SID sectors, each SID sector in said first groupof SID sectors including ERC values for use during write operations andeach SID sector in said second group of SID sectors including ERC valuesfor use during read operations.
 23. The disk drive, as claimed in claim22, wherein: said SID sectors within said first group of SID sectors areoffset from a track centerline by a write microjog value and said SIDsectors within said second group of SID sectors are offset from thetrack centerline by a read microjog value.
 24. The disk drive, asclaimed in claim 15, wherein: said SID sectors within said first trackare non-uniformly distributed about said first track.
 25. The diskdrive, as claimed in claim 15, wherein: at least one of said SID sectorswithin said first track includes error data for use in detecting anerror in data read from said SID sector.
 26. The disk drive, as claimedin claim 15, wherein: said error data can be used to correct at leastone error in said data read from said SID sector.
 27. The disk drive, asclaimed in claim 15, wherein: each of said plurality of substantiallyconcentric tracks includes a plurality of servo sectors and a pluralityof customer data regions distributed therein, wherein a subgroup of saidplurality of customer data regions within each track includes a SIDsector for storing overhead data corresponding to a predetermined numberof servo sectors within said track.
 28. The disk drive, as claimed inclaim 23, wherein: said write microjog value is different from said readmicrojog value.
 29. A disk drive, comprising: a data storage disk havinga plurality of substantially concentric tracks, each of said pluralityof substantially concentric tracks having a plurality of servo sectorsand a plurality of customer data regions distributed therein; a spinmotor for rotating said data storage disk about an axis; a transducerfor use in transferring data between said data storage disk and anexterior environment, said transducer generating an analog read signalas a result of reading said data storage disk; an actuator assemblycoupled to said transducer for use in moving said transducer to a targettrack of said data storage disk to perform a data transfer with thetarget track, said actuator assembly including an actuator arm forsupporting said transducer and a motor unit for controllably moving saidactuator arm in response to a control signal; a data channel, coupled tosaid transducer, for receiving said analog read signal from saidtransducer and converting said analog read signal to a digital format,said data channel having a serial output and a parallel output; and acontroller for controlling operation of said disk drive, said controllerreceiving transducer position information read from a servo sector ofsaid data storage disk via said serial output of said data channel andoverhead data read from a customer data region of said data storage diskvia said parallel output of said data channel, said overhead dataincluding data corresponding to multiple servo sectors on said datastorage disk, wherein said controller uses said overhead data to enhancedisk drive performance.
 30. The disk drive, as claimed in claim 29,wherein: said overhead data includes embedded runout correction (ERC)data corresponding to multiple servo sectors on said data storage disk.31. The disk drive, as claimed in claim 29, wherein: said controllerincludes a buffer memory for temporarily storing overhead data receivedfrom said parallel output of said data channel.
 32. The disk drive, asclaimed in claim 31, wherein: said controller retrieves a portion ofsaid overhead data from said buffer memory in connection with traversalof a corresponding servo sector of said data storage disk by saidtransducer.
 33. A method for performing a multi-track sequential diskoperation in a disk drive, comprising the steps of: first transferringcustomer data between a first transducer and multiple customer datasectors on a first track in the disk drive in a sequential manner,wherein said multiple customer data sectors occur within a plurality ofcustomer data regions on said first track; reading a SID sector within acustomer data region of said first track using said first transducer,said SID sector including overhead data corresponding to a group ofservo sectors within a sequential second track in the disk drive,wherein said second track is different from said first track; storingthe overhead data read from the SID sector in a memory; secondtransferring customer data between a second transducer and multiplecustomer data sectors on said second track in the disk drive in asequential manner; and using said overhead data stored in said memory inresponse to traversal by said second transducer of servo spokes on saidsecond track to enhance disk drive performance.
 34. The method, asclaimed in claim 33, wherein: said first and second tracks are locatedon different disk surfaces within the disk drive and said first andsecond transducers are different.
 35. The method, as claimed in claim33, wherein: said first and second tracks are located on the same disksurface within the disk drive and said first and second transducers arethe same.
 36. The method, as claimed in claim 33, wherein: said step offirst transferring includes reading blocks of customer data from saidmultiple customer data sectors on said first track using said firsttransducer.
 37. The method, as claimed in claim 33, wherein: said stepof first transferring includes writing blocks of customer data to saidmultiple customer data sectors on said first track using said firsttransducer.
 38. The method, as claimed in claim 33, wherein: said stepof second transferring occurs after said first transducer has reached alast customer data sector on said first track during said step of firsttransferring.
 39. A disk drive comprising: a data storage disk having aplurality of tracks, a first track within said plurality of trackshaving a plurality of servo sectors and a plurality of customer dataregions distributed therein, a subgroup of said plurality of customerdata regions each including a SID sector for storing overhead datacorresponding to a predetermined number of servo sectors on said firsttrack, wherein multiple SID sectors within said first track includeoverhead data corresponding to a first servo sector within said firsttrack; and, a transducer for reading said overhead data, wherein saidoverhead data is used to position said transducer relative to said datastorage disk.
 40. The disk drive, as claimed in claim 39, wherein: acurrent SID sector within said first track includes a digital valuespecifying the number of servo sectors between said current SID sectorand a subsequent SID sector.
 41. A disk drive, comprising: a datastorage disk having a plurality tracks, each of said plurality of trackshaving a plurality of servo sectors and a plurality of customer dataregions distributed therein; a transducer which generates an analog readsignal as a result of reading said data storage disk; a data channel,coupled to said transducer, for receiving said analog read signal fromsaid transducer and converting said analog read signal to a digitalformat, said data channel having a serial output and a parallel output;and a controller for controlling operation of said disk drive, saidcontroller receiving transducer position information read from a servosector of said data storage disk via said serial output of said datachannel and overhead data read from a customer data region of said datastorage disk via said parallel output of said data channel, saidoverhead data being used to position said transducer relative to saiddata storage disk.
 42. A disk drive comprising: a data storage diskhaving a plurality of tracks, a first track within said plurality oftracks having a plurality of servo sectors and a plurality of customerdata regions distributed therein, a subgroup of said plurality ofcustomer data regions each including a SID sector for storing overheaddata corresponding to a predetermined number of servo sectors on saidfirst track, wherein each SID sector within said first track includes avalue which varies with, and is indicative of, a distance to asubsequent SID sector within said first track; and, a transducer forreading said overhead data, wherein said overhead data is used toposition said transducer relative to said data storage disk.
 43. Thedisk drive, as claimed in claim 42, wherein: said overhead data includesembedded runout correction (ERC) data.
 44. A disk drive comprising: adata storage disk having a plurality of substantially concentric tracks,a first track within said plurality of substantially concentric trackshaving a plurality of servo sectors and a plurality of customer dataregions distributed therein, a subgroup of said plurality of customerdata regions each including a SID sector for storing overhead datacorresponding to a predetermined number of servo sectors on said firsttrack, wherein multiple SID sectors within said first track includeoverhead data corresponding to a first servo sector within said firsttrack, wherein said SID sectors within said first track each include anembedded run out correction (ERC) value for each of said predeterminednumber of servo sectors associated with said SID sector, and whereinsaid SID sectors within said first track are divided into a first groupof SID sectors and a second group of SID sectors, each SID sector insaid first group of SID sectors consisting of ERC values for use duringwrite operations and each SID sector in said second group of SID sectorsconsisting of ERC values for use during read operations; a spin motorfor rotating said data storage disk about an axis; a transducer for usein transferring data between said data storage disk and an exteriorenvironment; an actuator assembly coupled to said transducer for use inmoving said transducer to a target track of said data storage disk toperform a data transfer with said target track, said actuator assemblyincluding an actuator arm for supporting said transducer and a motorunit for controllably moving said actuator arm in response to a controlsignal; and a controller for controlling the operation of said diskdrive, said controller receiving overhead data read from a first SIDsector on said first track by said transducer and using said overheaddata to control said disk drive in response to subsequent traversal bysaid transducer of each of said predetermined number of servo sectorsassociated with said first SID sector.
 45. The disk drive, as claimed inclaim 44, wherein: said SID sectors within said first group of SIDsectors are offset from a track centerline by a write microjog value andsaid SID sectors within said second group of SID sectors are offset fromthe track centerline by a read microjog value.
 46. The disk drive, asclaimed in claim 45, wherein: said write microjog value is differentfrom said read microjog value.
 47. A disk drive comprising: a datastorage disk having a plurality of substantially concentric tracks, afirst track within said plurality of substantially concentric trackshaving a plurality of servo sectors and a plurality of customer dataregions distributed therein, at least two of said plurality of customerdata regions including a SID sector for storing overhead datacorresponding to a predetermined number of servo sectors on said firsttrack, wherein said SID sectors within said first track are divided intoa first group of SID sectors and a second group of SID sectors, each SIDsector in said first group of SID sectors including ERC values for useduring write operations but not read operations and each SID sector insaid second group of SID sectors including ERC values for use duringread operations but not write operations; and, a transducer for readingsaid overhead data, wherein said overhead data is used to position saidtransducer relative to said data storage disk.
 48. The disk drive, asclaimed in claim 47, wherein: said SID sectors within said first groupof SID sectors are offset from a track centerline by a write microjogvalue and said SID sectors within said second group of SID sectors areoffset from the track centerline by a read microjog value.
 49. The diskdrive, as claimed in claim 28, wherein: said write microjog value isdifferent from said read microjog value.
 50. A disk drive comprising: adata storage disk having a plurality of tracks, each of said trackshaving a plurality of servo sectors and a plurality of customer dataregions, said plurality of servo sectors including data that is recordedat a first frequency and said plurality of customer data regionsincluding data that is recorded at a second frequency that is differentfrom said first frequency, wherein at least one of said customer dataregions on said data storage disk includes a dedicated portion forstoring overhead data on said data storage disk, said overhead databeing stored at said second frequency; and, a transducer for readingsaid overhead data, wherein said overhead data includes servo sectoridentification information.
 51. A disk drive comprising: a data storagedisk having a plurality of substantially concentric tracks, each of saidplurality of substantially concentric tracks having a plurality of servosectors and a plurality of customer data regions distributed therein,said plurality of servo sectors including data that is recorded at afirst frequency and said plurality of customer data regions includingdata that is recorded at a second frequency that is different from saidfirst frequency, wherein at least one of said customer data regions onsaid data storage disk includes a dedicated portion for storing overheaddata corresponding to multiple servo sectors on said data storage diskand wherein said at least one customer data region is located on adifferent track from said multiple servo sectors, said overhead databeing recorded at said second frequency; and, a transducer for readingsaid overhead data from said data storage disk.